Various functional devices used in electronic devices such as MEMS elements are delicate parts having a sensitive portion or a driving portion and are hermetically-sealed and packaged to prevent deterioration in function due to sticking of particles or the like in many cases. Such an hermetically-sealed package is produced in such a manner that a substrate mounted with semiconductor elements and a cover are bonded to each other by use of a sealing material, thereby being sealed.
As a sealing material used in the production of the hermetically-sealed package, a brazing material (for example, Au—Sn-based brazing material) was widely applied in the past. However, since such a brazing material had a high bonding temperature (melting temperature of the brazing material), a material capable of bonding at a lower temperature was required. Against such background, the present inventors have developed a sealing method of using a metal paste, as a technique capable of bonding at a low temperature and having excellent sealing properties (Patent Document 1). In this method, a metal paste containing predetermined metal powders is applied, and a metal powder sintered body obtained by sintering the metal paste is used as a sealing material. The metal powder sintered body is further densified when being heated and pressurized at the time of bonding (sealing) and has substantially the same densification as a bulk body, whereby it can act as a sealing material.